Image forming apparatus

ABSTRACT

A image forming apparatus includes: an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; a controller configured to execute a mode of outputting a test chart for setting a voltage to be applied to the transfer member during image formation, the mode being a mode of transferring a plurality of test images to the test chart by applying a plurality of different voltages to the transfer member; and an operation portion capable of setting a type of a sheet on which the mode is executed; wherein the controller is configured to preset a voltage value for setting a voltage to be applied when the test images are transferred in the mode based on a voltage value, which is set in the previous mode.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image forming apparatus such as anelectrophotographic copying machine and an electrophotographic printer(for example, a laser beam printer, an LED printer, etc.).

Description of the Related Art

A configuration of an electrophotographic system image forming apparatusis widely known in which a full-color toner image formed by superposingyellow, magenta, cyan, and black toner images is transferred to a sheetby applying a voltage to a transfer member to form an image.

Japanese Patent Laid-Open No. 2000-221803 describes a configuration inwhich such an image forming apparatus executes a mode of adjusting atransfer voltage to be applied to a transfer member. In this mode, thetransfer voltage to be applied to the transfer member is switched toform a plurality of patch images on the sheet, and the user checks thetransferability of the patch images and sets an optimum transfervoltage.

Japanese Patent Laid-Open No. 2004-280003 describes a configuration inwhich a transfer voltage serving as a reference for forming a patchimage can be set by a user in a mode of adjusting the transfer voltage.

However, in the configuration described in Japanese Patent Laid-Open No.2004-280003, in order to use a result of the mode executed in the pastwhen setting the transfer voltage as the reference for forming the patchimage, the result of the mode needs to be recalled by a call button,which is troublesome for a user.

SUMMARY OF THE INVENTION

It is desirable to provide an image forming apparatus that can easilyuse a result of a mode in the past in a mode of adjusting a transfervoltage.

A representative configuration of the present invention is as follows:

a image forming apparatus includes:

an image bearing member;

a transfer member configured to transfer a toner image carried on theimage bearing member to a sheet by being applied with a voltage;

a controller configured to execute a mode of outputting a test chart forsetting a voltage to be applied to the transfer member during imageformation, the mode being a mode of transferring a plurality of testimages to the test chart by applying a plurality of different voltagesto the transfer member; and

an operation portion capable of setting a type of a sheet on which themode is executed;

wherein the controller is configured to preset a voltage value forsetting a voltage to be applied when the test images are transferred inthe mode based on a voltage value, which is set in the previous mode.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an image formingapparatus;

FIG. 2 is a block diagram illustrating a part of a system configurationof the image forming apparatus;

FIG. 3 is a flowchart of a setting mode;

FIG. 4A and FIG. 4B are diagrams each illustrating a display screen ofan operation portion;

FIG. 5A and FIG. 5B are diagrams each illustrating a state in which apatch image is formed on a sheet;

FIG. 6 is a schematic cross-sectional view of an image formingapparatus;

FIG. 7 is a schematic diagram of a spectroscopic sensor;

FIG. 8A and FIG. 8B are diagrams each illustrating a status A filter andvisual spectral characteristics; and

FIG. 9 is a flowchart of a setting mode.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

<Image Forming Apparatus>

First, the overall configuration of the image forming apparatusaccording to the first embodiment of the present invention will bedescribed with reference to the drawings together with an operationduring image formation. Note that the dimensions, materials, shapes, andrelative arrangements of the described components are not intended tolimit the scope of the present invention only to those unless otherwisespecified.

The image forming apparatus A transfers yellow, Y magenta M, cyan C, andblack K toners to an intermediate transfer belt, and then transfersimages to a sheet to form an image. Note that, in the followingdescription, the members that use the toners of the above-describedrespective colors are associated with letters Y, M, C, and K, but theconfiguration and operation of each member are substantially the sameexcept that the colors of the toner to be used are different from eachother. Therefore, these letters are omitted as appropriate unlessdistinction is required.

As illustrated in FIG. 1, the image forming apparatus A includes animage forming portion 40 configured to transfer a toner image onto asheet S to form an image, and a sheet feeding portion, not illustrated,configured to feed the sheet toward the image forming portion 40, and afixing device 46 as a fixing portion configured to fix the toner imageon the sheet. Note that examples of the sheet S used for image formationinclude a plain paper, a synthetic resin sheet, a cardboard, an overheadprojector sheet.

The image forming portion 40 includes a photosensitive drum 51 (51Y,51M, 51C, 51K) and a rubber charging roller 52 (52Y, 52M, 52C, 52K)configured to charge the surface of the photosensitive drum 51. Further,a laser scanner unit 42 (42Y, 42M, 42C, 42K) and a developing device 20(20Y, 20M, 20C, 20K) are provided. Also, a drum cleaner 55 (55Y, 55M,55C, 55K), a pre-exposure device 54 (54Y, 54M, 54C, 54K), and anintermediate transfer unit 44 are provided.

The intermediate transfer unit 44 includes a primary transfer roller 47(47Y, 47M, 47C, 47K), an intermediate transfer belt 50 (image bearingmember), a secondary transfer roller 61, a secondary transfer counterroller 62, a tension roller 82, a driving roller 81, and a belt cleaner80.

The photosensitive drum 51 (photosensitizer, photosensitive member) is anegatively charged organic photosensitizer (OPC) having an outerdiameter of 30 mm. The photosensitive drum 51 has a three-layerstructure in which an undercoat layer, a photocharge generation layer,and a charge transport layer are sequentially coated on an outerperipheral surface of an aluminum cylinder.

The developing device 20 includes an aluminum developing sleeve 24 (24Y,24M, 24C, 24K). Inside the developing sleeve 24, a magnet roller, notillustrated, is included in a non-rotating state. The developing sleeve24 bears a developer containing non-magnetic toner and a magneticcarrier and conveys the developer to a developing region at a positionfacing the photosensitive drum 51. Note that, when the developer in thedeveloping device 20 decreases, an additional developer is supplied fromtoner bottle 41 (41Y, 41M, 41C, 41K) to the developing device 20.

The primary transfer roller 47 includes an elastic layer of ionconductive foamed rubber (NBR rubber) and a metal core, has an outerdiameter of 15 to 20 mm, and an electrical resistance of 1×10⁵ to 1×10⁸Ω(measurement environment: 23° C., 50% RH, applied voltage 2 kV).

The intermediate transfer belt 50 is stretched by a tension roller 82, asecondary transfer counter roller 62, and a driving roller 81 androtates around the driving roller 81 as the driving roller 81 rotates.The tension roller 82 pushes the intermediate transfer belt 50 outwardby a biasing force of a spring, not illustrated. Accordingly, a tensionon the order of 2 to 5 kg is applied to the intermediate transfer belt50.

The intermediate transfer belt 50 includes three layers: a base layer,an elastic layer, and a surface layer. In the present embodiment, thepolyimide base layer has a thickness of 85 μm, the elastic layer made ofCR rubber containing an ionic conductive agent and carbon black has athickness of 260 μm, and the surface layer made of urethane containingPTFE has a thickness of 2 μm. The intermediate transfer belt 50 has aninitial volume resistivity of 5×10⁹ Ω·cm and an MD1 hardness of 70degrees.

Note that the base layer is made of a material containing an appropriateamount of carbon black as an antistatic agent in resins such aspolyimide and polycarbonate or various rubbers, and has a thickness of0.05 mm to 0.15 mm. The elastic layer is made of a material obtained byadding an appropriate amount of the ionic conductive agent to variousrubbers such as urethane rubber and silicone rubber, and has a thicknessof 0.1 mm to 0.500 mm in terms of followability to irregularity on thesheet S and durability of the sheet S. The surface layer is made of, forexample, a single type of resin material such as polyurethane,polyester, and epoxy resin, or two or more types of elastic materialssuch as elastic material rubber, elastomer, butyl rubber, etc., as thebase material, and the thickness is 0.0002 mm to 0.020 mm. In addition,in consideration of the transferability of the toner to the sheet S, forexample, one or two, or more types of powders or particles such as afluororesin or a material having a different particle size are dispersedin this base material as a material for improving the lubricity to formthe surface layer.

The intermediate transfer belt 50 has a volume resistivity of 5×10⁸ to1×10¹⁴ Ω·cm (measuring environment: 23° C., 50% RH) and a hardness of 60to 85° in MD1 hardness (measuring environment: 23° C., 50% RH). Thecoefficient of static friction is 0.15 to 0.6 (measuring environment:23° C., 50% RH, measuring instrument: type 94i manufactured by HEIDON).

The secondary transfer roller 61 is abutted and disposed on an outerperipheral surface of the intermediate transfer belt 50. The secondarytransfer roller 61 includes a metal core and an elastic layer of ionconductive foamed rubber (NBR rubber), and is a roller having an outerdiameter of 20 to 25 mm. The electrical resistance of the secondarytransfer roller 61 is adjusted to 1×10⁵ to 1×10⁸Ω (N/N (23° C., 50% RHmeasurement), 2 kV applied).

Next, an image forming operation will be described. The image formingapparatus A is configured to be capable of executing a mode of forming atoner image of each color on each of the four photosensitive drums 51 toform a full color image, and a monochrome mode of forming a black tonerimage on the photosensitive drum 51K to form an image of a single blackcolor. Hereinafter, a mode of forming a full-color image will bedescribed.

First, when the controller 30 illustrated in FIG. 2 receives an imageforming job signal, a sheet S is fed from a stack of sheets stored in asheet cassette, not illustrated, by a feeding roller, not illustrated.Subsequently, the sheet S is conveyed by a registration roller 83 to asecondary transfer portion N formed by the secondary transfer roller 61and the secondary transfer counter roller 62.

In contrast, in the image forming portion 40, first, a DC voltage isapplied to the charging roller 52, so that the surface of thephotosensitive drum 51 in contact with the charging roller 52 ischarged. Subsequently, the laser scanner unit 42 irradiates the surfaceof the photosensitive drum 51 with a laser beam in accordance with animage signal transmitted from a host device such as an original readingdevice or a personal computer, not illustrated, or an external devicesuch as a digital camera or a smartphone. Accordingly, an electrostaticlatent image is formed on the surface of the photosensitive drum 51.

Subsequently, a DC voltage is applied to the developing sleeve 24 of thedeveloping device 20, so that toner is attached to the electrostaticlatent image formed on the surface of the photosensitive drum 51, sothat a toner image is formed on the surface of the photosensitive drum51. The toner image formed on the surface of the photosensitive drum 51in this manner is sent to a primary transfer portion formed from thephotosensitive drum 51 and the primary transfer roller 47.

A primary transfer voltage having a positive polarity opposite to acharging polarity of the toner is applied to the primary transfer roller47, so that the toner image sent to the primary transfer portion isprimarily transferred to the intermediate transfer belt 50. Accordingly,the toner images of the respective colors are sequentially superimposedon the intermediate transfer belt 50 to form a full-color toner image.

Subsequently, the toner image is sent to the secondary transfer portionN by a rotation of the intermediate transfer belt 50. Then, in thesecondary transfer portion N, a secondary transfer voltage having apolarity opposite to the charging polarity of the toner and beingcontrolled to a constant voltage is applied to the secondary transferroller 61, so that the toner image on the intermediate transfer belt 50is secondarily transferred to the sheet S.

In the present embodiment, constant voltage control is used to controlthe secondary transfer voltage, a DC voltage on the order of +1 kV to +7kV is applied as the secondary transfer voltage, and a secondarytransfer current on the order of +40 μA to +120 μA is passed. The metalcore of the secondary transfer counter roller 45 a is connected to theground potential. Note that in the present embodiment, a configurationis described in which a voltage is applied to the secondary transferroller 45 b to perform secondary transfer, but a configuration in whicha voltage is applied to the secondary transfer counter roller 45 a toperform the secondary transfer is also applicable.

The sheet S having the toner image transferred thereto is sent to thefixing device 46. Then, the toner image is fixed on the sheet S by beingheated and pressurized by the fixing device 46. Subsequently, the sheetS is discharged to the outside of the image forming apparatus A.

Note that after the primary transfer of the toner image from thephotosensitive drum 51 to the primary transfer roller 47, the surface ofthe photosensitive drum 51 is neutralized by the pre-exposure device 54.Subsequently, the toner remaining on the surface of the photosensitivedrum 51 is scraped off and removed by the drum cleaner 55 configured toabut the photosensitive drum 51 with a predetermined pressing force.Further, the toner remaining on the intermediate transfer belt 50 afterthe secondary transfer is removed by the belt cleaner 80.

<Controller>

Next, an outline of the system configuration of the image formingapparatus A will be described.

FIG. 2 is a block diagram illustrating a part of the systemconfiguration of the image forming apparatus A. As illustrated in FIG.2, the image forming apparatus A includes a controller 30 having a CPU31, a ROM 32, a RAM 33, and an input/output circuit 34.

The ROM 32 stores various data such as control programs and tables. TheCPU 31 performs various types of arithmetic processing based on thecontrol program and information stored in the ROM 32. The RAM 33temporarily stores data.

That is, in the controller 30, the CPU 31 controls each device of theimage forming apparatus A while using the RAM 33 as a work area based onthe control program stored in the ROM 32. Then, the above-describedimage forming operation such as toner image formation on thephotosensitive drum 51 is executed through the control of each device.

The input/output circuit 34 inputs and outputs a signal to and from theoutside. The CPU 31 is connected to a sheet feeding portion, notillustrated, an image forming portion 40 and an operation portion 70,described later, via the input/output circuit 34 and performs control byexchanging signals with each portion.

An operation portion 70 is connected to the controller 30. The operationportion 70 is a touch panel member including operation buttons arrangedon a screen of a liquid crystal panel. The user can perform varioussettings related to image formation and execute an image forming job byoperating the operation portion 70. The controller 30 receives a signalfrom the operation portion 70 and operates various devices of the imageforming apparatus A.

The controller 30 is connected to a temperature sensor 71 configured todetect an in-machine temperature and a humidity sensor 72 configured todetect the in-machine humidity. The temperature detected by thetemperature sensor 71 and the humidity detected by the humidity sensor72 are entered to the controller 30 as signals.

The controller 30 includes a charging power source 73 configured toapply a voltage to the charging roller 52, a developing power source 74configured to apply a voltage to the developing sleeve 24, a primarytransfer power source 75 configured to apply a voltage to the primarytransfer roller 47, and a secondary transfer power source 76 configuredto apply a voltage to the secondary transfer roller 61. The controller30 controls these power supplies and applies a voltage to each member.

A voltage sensor 75 a and a current sensor 75 b are connected to theprimary transfer power source 75. The voltage sensor 75 a detects thevalue of the voltage applied from the primary transfer power source 75to the primary transfer roller 47. The current sensor 75 b detects thevalue of the primary transfer current that flows when a voltage isapplied from the primary transfer power source 75 to the primarytransfer roller 47. Note that four primary transfer power sources 75,four voltage sensors 75 a and four current sensors 75 b are providedcorresponding to the four primary transfer rollers 47, respectively. Thecontroller 30 can individually control these members.

Further, a voltage sensor 76 a and a current sensor 76 b are connectedto the secondary transfer power source 76. The voltage sensor 76 adetects the value of the voltage applied from the secondary transferpower source 76 to the secondary transfer roller 61. The current sensor76 b (current detecting unit) detects the value of the secondarytransfer current that flows when a voltage is applied from the secondarytransfer power source 76 to the secondary transfer roller 61.

<ATVC Control>

In the secondary transfer process, a current flow from the secondarytransfer roller 61 to the secondary transfer counter roller 62 via theintermediate transfer belt 50. Here, as the image forming apparatus A isused, the electrical resistances of the secondary transfer roller 61,the intermediate transfer belt 50, and the secondary transfer counterroller 62 vary. For this reason, if it is desired to flow a desiredsecondary transfer current in the secondary transfer process, it isnecessary to correct the value of the voltage applied to the secondarytransfer roller 61 in accordance with variations in the electricalresistance.

Therefore, the image forming apparatus A performs ATVC control (anothermode) that corrects the value of the secondary transfer voltageaccording to variations in electrical resistance of the secondarytransfer roller 61, the intermediate transfer belt 50, and the secondarytransfer counter roller 62. Hereinafter, the ATVC control will bedescribed.

The ATVC control is performed during non-image formation. First, thecontroller 30 applies several types of voltages from the secondarytransfer power source 76 to the secondary transfer roller 61. At thistime, the voltage sensor 76 a detects several types of voltage valuesapplied to the secondary transfer roller 61, respectively. The currentsensor 76 b detects the value of the current that flows when severaltypes of voltages are applied to the secondary transfer roller 61. Next,the controller 30 determines a value of the secondary transfer voltageVb that allows a target current to be output in the secondary transferprocess to flow based on the relationship between the values of severaltypes of voltages applied to the secondary transfer roller 61 and thecurrent values flowing at that time.

For example, first, a voltage ε1 is applied from the secondary transferpower source 76 to the secondary transfer roller 61, and the current ω1flowing at that time is detected by the current sensor 76 b. If thecurrent value detected by the current sensor 76 b is smaller than thetarget current value, the voltage ε2 larger than the voltage ε1 is nextapplied from the secondary transfer power source 76 to the secondarytransfer roller 61, and the current ω2 flowing at that time is detectedby the current sensor 76 b. Subsequently, the relationship between thevoltage ε1 and the current ω1 and the relationship between the voltageε2 and the current ω2 are linearly approximated to obtain the value ofthe secondary transfer voltage Vb that allows the target current toflow. Note that the types of voltages to be applied are not limited totwo but may be three or more.

In the secondary transfer process, a secondary transfer current flowsfrom the secondary transfer roller 61 to the secondary transfer counterroller 62 via the intermediate transfer belt 50 and the sheet S. Forthis reason, the impedance becomes higher by the amount of the sheet Sthan when ATVC control is executed. Therefore, at the secondary transfervoltage Vb determined by the ATVC control, a desired secondary transfercurrent cannot be passed, thereby resulting in a transfer failure.

Therefore, in consideration of the increase in impedance due to thesheet S, a divided voltage Vp of the sheet S, which is a voltagenecessary for flowing a desired secondary transfer current, is appliedin addition to the secondary transfer voltage Vb determined by ATVCcontrol. That is, in the secondary transfer process, a voltage of Vb+Vpis applied as the secondary transfer voltage.

The ROM 32 stores a table, not illustrated, in which a type and a basisweight of the sheet S, a temperature and a humidity inside the imageforming apparatus A, and a value of the divided voltage Vp of the sheetS are associated with each other. The controller 30 refers to the table,not illustrated, and determines the divided voltage Vp from the type andthe basis weight of the sheet S selected by the user operating theoperation portion 70 or a personal computer, and the temperature andhumidity in the apparatus detected by the temperature sensor 71 and thehumidity sensor 72.

<Setting Mode>

As described above, the value of the secondary transfer voltage isdetermined by ATVC control and the table, not illustrated. However, ifthe moisture content and electrical resistance of the sheet S used forimage formation are significantly different from those of a standardsheet, the desired secondary transfer current does not flow at the valueof the divided voltage Vp set in the table, not illustrated, which mayresult in a transfer failure. For example, if the moisture content ofthe sheet S used for image formation is significantly lower than that ofa standard sheet, abnormal electric discharge may occur when secondarytransfer is performed with the divided voltage Vp set in the table, notillustrated.

Therefore, the image forming apparatus A executes a setting mode forsetting an appropriate secondary transfer voltage. In the setting mode,the image forming apparatus A adjusts the secondary transfer voltage inaccordance with the type and the moisture content of the sheet S usedfor image formation. Hereinafter, this setting mode will be describedwith reference to the flowchart illustrated in FIG. 3.

As illustrated in FIG. 3, the user first operates the operation portion70 (sheet setting portion) to select a sheet cassette, not illustrated,in which the sheet S used for image formation is stored (S1).Accordingly, the type and the size of the sheet S are specified. Here,the type and size of the sheet S accommodated in the sheet cassette canbe stored and registered in the ROM 32 for each sheet cassette by theuser operating the operation portion 70. In the present embodiment, as aregistration method, three types of methods; a method of registering thesheet S according to the size and the basis weight such as A3 plainpaper or A4 cardboard, a method of registering the sheet S by brandinformation, and a method of registering the sheet S by the userdirectly entering the size and the basis weight may be employed. Notethat a plurality of items of the brand information is registered inadvance in the ROM 32, and the user selects a brand of the sheet S fromthe registered information. When the type and the size of the sheet Sare designated, the appearance of the display screen of the operationportion 70 is as the screen illustrated in FIG. 4A (S2).

Next, on the screen illustrated in FIG. 4A of the operation portion 70,the user sets a secondary transfer voltage range for forming a patchimage to be described later (S4). Specifically, the reference value(center value) of the secondary transfer voltage when a patch image isformed is set at ±20 levels. That is, the operation portion 70 is avoltage setting portion configured to set the value of the secondarytransfer voltage when a patch image is formed. Here, if “0” is selectedas the reference value, a value obtained by adding the secondarytransfer voltage Vb set by the above-described ATVC control to thedivided voltage Vp set in the table, not illustrated, stored in the ROM32 about the sheet S is selected as a value for the secondary transfervoltage. That is, the ROM 32 stores data in which the type and size ofthe sheet S are associated with the reference value of the secondarytransfer voltage when the patch image is formed in the setting mode. Onthe screen illustrated in FIG. 4A, the reference values stored in theROM 32 associated with the type and size of the sheet S specified instep S1 are displayed by default. Note that when the image formingapparatus A is shipped, the reference value associated with all typesand sizes of sheets S is “0”.

In the present embodiment, one level corresponds to 150 V. For thisreason, for example, if “+1” is selected as the reference value, thevoltage obtained by adding 150 V to the value of the divided voltage Vpset in the table, not illustrated, for the sheet S and the secondarytransfer voltage Vb set by ATVC control corresponds to the referencevalue. That is, in the present embodiment, the reference value of thesecondary transfer voltage when a patch image is formed can be set inthe range of 3000 V. Note that the voltage value corresponding to onelevel and the number of levels that can be set are not limited to thenumerical values described above and may be other numerical values.

Next, whether to perform the setting mode ion one side or on both sidesof the sheet S is set (S5). Subsequently, when the user presses the“output test page” button illustrated in FIG. 4A, the secondary transfervoltage is switched at ±5 level with respect to the reference value, andeleven patch images (test images) are transferred to the sheet S (S6).That is, the controller 30 transfers the plurality of patch images tothe sheet S by switching the secondary transfer voltage to be applied tothe secondary transfer roller 61 by 150 V (predetermined value) within apredetermined range centering on the reference value. That is, thecontroller 30 applies a plurality of different voltages to the secondarytransfer roller 61 and outputs a plurality of patch images to betransferred when the plurality of voltages is applied. In this manner, atest chart that is the sheet S on which a plurality of patch images isformed is output.

For example, if a double-side coated sheet having a basis weight of 350g/m² and an A3 size is selected as the sheet S to be used for imageformation and the reference value is “0”, the reference secondarytransfer voltage value is 2500 V. Therefore, eleven patch images areformed with the secondary transfer voltages switched from 1750 V to 3250V by 150 V with reference to 2500 V.

Note that the lower limit value of the secondary transfer voltage levelwhen a patch image is formed is “−20”, and the upper limit value is“+20”. For this reason, for example, even if “+17” is selected as thereference value, a patch image of a level higher than “+20” is notformed, and for the part exceeding “+20”, patch images of “+20” arerepeatedly formed. That is, one patch images each from “+12” to “+19”are formed, and three patch images “+20” are formed.

FIG. 5A is a diagram illustrating a state in which a patch image isformed on a sheet S having a length of 420 to 487 mm in the conveyancedirection. FIG. 5B is a diagram illustrating a state in which a patchimage is formed on the sheet S having a length of 210 to 419 mm in thetransport direction. As illustrated in FIG. 5, the level of thesecondary transfer voltage is described in the vicinity of each patchimage. If eleven patch images do not fit on one sheet S, patch imagesare formed on two sheets S. Note that in the present embodiment, ifpatch images are formed on an A4 size sheet S, since eleven patch imagescannot fit on two sheets S, 10 patch images are exceptionally formed onthe sheet S.

Here, the size of the patch image needs to be a size that allows theuser to easily determine the transferability. The transferability of ablue solid image and a black solid image is difficult to discriminate ifthe size of the patch image is small. Therefore, the size of the patchimage is preferably 10 mm square or more, and more preferably 25 mmsquare or more.

Next, when the user selects the “OK” button illustrated in FIG. 4A, thescreen illustrated in FIG. 4B is displayed. The user selects a patchimage having the optimum transferability from the eleven patch imagesformed on the sheet S. Then, on the screen illustrated in FIG. 4B, thelevel of the secondary transfer voltage written together with theselected patch image is entered (S7, S8). That is, the operation portion70 is a selecting portion configured to enter the selected patch image(selected image). Subsequently, when the user presses the “OK” buttonillustrated in FIG. 4B, the controller 30 sets the secondary transfervoltage corresponding to the selected level as the secondary transfervoltage to be applied during normal image formation and exits thesetting mode (S9).

Here, the value of the secondary transfer voltage is increased stepwisefrom the smaller value, and a voltage at which the toner is transferredin a secondary color such as blue is a guideline for the lower limitvalue. Further, the voltage value is further increased from this lowerlimit value, and the voltage at which image defects occur in the blacksolid image and the halftone portion is a guideline for the upper limitvalue. When the user sets the level of the secondary transfer voltagewithin the range between the upper limit value and the lower limitvalue, desirable transferability is easily obtained.

If there is no patch image having optimum transferability among theeleven patch images formed on the sheet S, the process returns to stepS4, and the user again selects the reference value of the secondarytransfer voltage when the patch image is formed. Subsequently, a patchimage is output in the same manner as described above, a patch imagehaving an optimum transferability is selected, and a level is entered(S5 to S8). Subsequently, the “OK” button illustrated in FIG. 4B isselected and exits the setting mode (S9).

In this manner, in the setting mode, the controller 30 sets a voltage tobe applied from the secondary transfer power source 76 to the secondarytransfer roller 61 during image formation based on the voltagecorresponding to the patch image selected by the user from the pluralityof patch images transferred to the sheet S. Accordingly, even if themoisture content and electrical resistance of the sheet S used for imageformation are greatly different from those of a standard sheet,desirable transferability can be ensured.

Here, if the type and the size of the sheet S specified in step S1 inthe setting mode in the past and the type and size of the sheet S set instep S1 in the current setting mode are the same, the controller 30performs the next control. That is, the secondary transfer voltage levelset on the screen illustrated in FIG. 4B in the setting mode in the pastis displayed on the screen illustrated in FIG. 4A as a default settingof a reference value of the secondary transfer voltage when a patchimage is formed in the setting mode of this time (S2, S3). That is, thesecondary transfer voltage to be applied during image formation set inthe previous setting mode is set as a reference value (center value) ofthe secondary transfer voltage when a patch image is formed in the nextsetting mode. That is, every time the setting mode is performed, the CPU31 rewrites the reference value of the secondary transfer voltage storedin the ROM 32 associated with the type and the size of the sheet Sspecified in step S1 to a level of the selected patch image in Step S8.From the next time onward, if the setting mode is executed for the sheetS, and on the screen illustrated in FIG. 4A, the reference valuerewritten on the ROM 32 is displayed as a default setting.

Subsequently, the user sets the reference value of the secondarytransfer voltage when forming the patch image in the same manner asdescribed above (S4). That is, the user can change the reference valuedisplayed as the default setting on the operation portion 70 to adifferent value by operating the operation portion 70. Note that thereference value displayed on the operation portion 70 as the defaultsetting in the setting mode after being rewritten in the ROM 32 may beconfigured so that the user cannot change it.

In this manner, if the sheet S to which the patch image is transferredis the same in the setting mode in the past and the setting mode of thistime, the controller 30 performs the following control. That is, basedon the result of adjustment of the voltage applied to the secondarytransfer roller 61 during image formation when the setting mode isperformed in the past, the controller 30 changes the default setting ofthe reference value of the secondary transfer voltage displayed on theoperation portion 70 when the patch image is formed in the setting modeof this time. In other words, the controller 30 is configured to preseta voltage value for setting a voltage to be applied when the patchimages are transferred in the setting mode based on a voltage value,which is set in the previous setting mode. Accordingly, if the userwants to finely adjust the secondary transfer voltage in the situationin which the installation environment of the image forming apparatus Aand the state of the sheet S are slightly changed, an optimum secondaryvoltage can be found easily without restarting the setting of thesecondary transfer voltage from the beginning. For this reason,prolongation of execution time of the setting mode can be suppressed.

In other words, in the setting in which the setting of the secondarytransfer voltage when the patch image is formed is initialized, thepatch image may need to be formed again because the optimum secondarytransfer voltage cannot be found when the patch image is formed. Incontrast, by reflecting the result of the setting mode executed in thepast as in the present embodiment, it is possible to suppressprolongation of execution time of the setting mode without repeating theformation of the patch image. Moreover, since the user can use theresult of the setting mode in the past with the default setting withoutcalling the result of the setting mode in the past, the result of thesetting mode in the past can be easily used, and the usability can beimproved.

Second Embodiment

Next, a second embodiment of the image forming apparatus A according tothe present invention will be described. Parts that are the same asthose in the first embodiment are not described specifically by usingthe same drawings and denoting the same reference numerals.

In the first embodiment, the controller 30 makes the operation portion70 display the secondary transfer voltage corresponding to the patchimage selected in the setting mode in the past as is as the level of thereference value of the secondary transfer voltage during patch imageformation in the setting mode of the next time. In contrast, in thepresent embodiment, the controller 30 makes the operation portion 70display a level corresponding to 80% of the secondary transfer voltagecorresponding to the patch image selected in the setting mode in thepast as the level of the reference value of the secondary transfervoltage during patch image formation in the setting mode of the nexttime.

For example, the level of the secondary transfer voltage correspondingto the patch image selected in the previous setting mode is assumed tobe “+15”. In this case, the controller 30 causes “+12” to be displayedas a default setting as a level of the reference value of the secondarytransfer voltage to be set when the patch image is formed on the screenillustrated in FIG. 4A in the setting mode for the next time.

The reason is as follows. That is, the cause of occurrence of thesecondary transfer failure often includes various factors in addition tovariations in installation environment of the image forming apparatus Aand variations in state of the sheet S. For this reason, an optimumsecondary transfer voltage is not always found by forming a patch imagebased on the secondary transfer voltage set in the setting mode of theprevious time. That is, an optimum secondary transfer voltage may befound within the limited number of patch images by suppressing the valueof the secondary transfer voltage value to be reflected.

Third Embodiment

Next, a third embodiment of the image forming apparatus A according tothe invention will be described. Parts that are the same as those in thefirst and second embodiments are not described specifically by using thesame drawings and denoting the same reference numerals.

FIG. 6 is a schematic cross-sectional view of the image formingapparatus A according to the present embodiment. As illustrated in FIG.6, in the image forming apparatus A of the present embodiment, anin-line spectroscopic sensor 90 configured to detect a patch image isprovided at a position downstream of the fixing device 46 in the sheetconveying direction. Other mechanical configurations are the same asthose of the first embodiment.

FIG. 7 is a schematic diagram of the spectroscopic sensor 90. Asillustrated in FIG. 7, the spectroscopic sensor 90 includes a white LED201 that irradiates light to the patch image T formed on the sheet S,and a diffraction grating 202 that disperses the reflected lightreflected from the patch image T for each wavelength. Further, thespectroscopic sensor 90 also includes the lens 206 configured to collectthe light irradiated from the white LED 201 on the patch image T andcollect the light reflected from the patch image T on the diffractiongrating 202.

Further, the spectroscopic sensor 90 includes a line sensor 203including a plurality of pixels that detects light separated for eachwavelength by the diffraction grating 202. The light intensity value ofeach pixel detected by the line sensor 203 is entered to the CPU 31 andsubjected to various types of calculation and stored in the ROM 32.

Four spectroscopic sensors 90 are arranged in the sheet width directionorthogonal to the conveyance direction of the sheet S. These fourspectroscopic sensors 90 individually detect a plurality of patch imagesformed at different positions in the sheet width direction. Note thatthe four spectroscopic sensors 90 may be used in such a manner that onepatch image is detected by some of the four spectroscopic sensors 90,and the results of detection are averaged.

The results of detection of the patch image performed by thespectroscopic sensors 90 are entered to the CPU 31 as spectralreflectance data, and a density calculation is performed in the CPU 31.In a conversion calculation from spectral reflectance data to densityvalue, a status A filter illustrated in FIG. 8A is used for yellow,magenta, and cyan patch images for the obtained spectral reflectance foreach wavelength. The visual spectral characteristic (Visual) illustratedin FIG. 8B are used for the black patch image. The status A filter andthe visual spectral characteristics are stored in the memory 31.

Further, the CPU 31 calculates a Lab value (chromaticity value) definedby the CIE (International Commission on Illumination) based on thespectral reflectance. The Lab values are calculated using a calculationmethod specified in ISO13655, with reference to the color matchingfunctions x(λ), y(λ), z(λ) specified in JIS Z8701, and the standardlight spectral distribution SD50(λ) specified in JIS Z8720.

Note that as a calibration process for the spectroscopic sensor 90,white LED light quantity adjustment using a white reference plate isperformed to correct into the reference spectral reflectance. For thiscalibration process, a known process can be arbitrarily used.

<Setting Mode>

Next, a setting mode using the spectroscopic sensor 90 according to thepresent embodiment will be described using a flowchart illustrated inFIG. 9. Note that in the following description, steps of performing thesame processes as those described with reference to FIG. 3 in the firstembodiment are denoted by the same reference numerals, and descriptionthereof is simplified.

As illustrated in FIG. 9, the user first operates the operation portion70 to select a sheet cassette, not illustrated, in which the sheet Sused for image formation is stored (S1). Next, if the type and the sizeof the specified sheet S are the same as those at the time of executionof the setting mode in the past, the level of the secondary transfervoltage set in the setting mode in the past is displayed as a defaultsetting of a reference value of the secondary transfer voltage when apatch image is formed in the setting mode of this time (S2, S3).

Next, when the patch image is formed, the user sets the reference value(center value) of the secondary transfer voltage and whether toimplement the setting mode in one side or both sides of the sheet S.(S4, S5). Next, when the user presses the “output test page” buttonillustrated in FIG. 4A, the secondary transfer voltage is switched at ±5level with respect to the reference value, and eleven patch images aretransferred to the sheet S (S6).

Next, the patch image formed on the sheet S is detected by thespectroscopic sensor 90 (S101). The spectroscopic sensor 90 outputsspectral reflectance data of each patch image to the controller 30. Thecontroller 30 converts the spectral reflectance of the black and gray(halftone) patch image into a density value, and converts the spectralreflectance of the blue patch image into a Lab value. Subsequently, thecontroller 30 selects a patch image in which these density value and theLab value are predetermined values stored in the ROM 31 in advance, andautomatically enter the level corresponding to the patch image as alevel of the secondary transfer voltage on the screen illustrated inFIG. 4B (S102). That is, the controller 30 causes the voltage applied tothe secondary transfer roller 61 during image formation determined basedon the result of detection performed by the spectroscopic sensor 90 tobe displayed on the screen of the operation portion 70 as a defaultsetting.

Note that if the density value and Lab value converted from the spectralreflectance of the patch image are not the predetermined value preset inthe ROM 32, the controller 30 selects the patch image having the densityvalue and Lab value closest to the predetermined value. However, in sucha case, the patch image may be formed again by changing the referencevalue of the secondary transfer voltage as in step S7 of the firstembodiment.

Next, on the screen illustrated in FIG. 4B, the user confirms the levelof the automatically entered secondary transfer voltage and presses the“OK” button if there is no problem. If the user wants to change thelevel of the secondary transfer voltage, it is achieved by manuallyentering the level and pressing the “OK” button. Accordingly, thecontroller 30 sets the secondary transfer voltage corresponding to theselected level as the secondary transfer voltage to be applied duringnormal image formation and exits the setting mode (S9). Note that thecontroller 30 may be configured not to display such a confirmationscreen but to set a voltage to be applied to the secondary transferroller 61 during image formation based on the result of detectionperformed by the spectroscopic sensor 90.

In this manner, in the present embodiment, the patch image is detectedby the spectroscopic sensor 90, and the controller 30 selects andautomatically enters the patch image according to the result ofdetection. Accordingly, the process of comparing patch images by theuser is omitted or simplified, and the setting of the secondary transfervoltage can be simplified.

Note that in the present embodiment, the controller 30 calculates thedensity value and Lab value of the patch image based on the spectralreflectance data output from the spectroscopic sensor 90 and selects thepatch image having the optimum transferability based on these values.However, the present invention is not limited thereto, and for example,the same effect as described above can be achieved even with aconfiguration in which the color difference V between the sheet S andthe patch image is obtained using the spectroscopic sensor 90 and thepatch image is selected based on the color difference V.

Here, the color difference V is a distance between two points in athree-dimensional space of the Lab and is calculated by the followingequation 1.

V=((L element of sheet S−L element of patch image T)²+(a element ofsheet S−a element of patch image T)²+(b element of sheet S−b element ofpatch image T)²)^(0.2)  (1)

In the present embodiment, although the spectroscopic sensor 90 is usedas the image detecting unit configured to detect the patch image, a CIStype or CCD type image sensor (optical sensor) may be used instead ofthe spectroscopic sensor 90. In this case, the image sensor detects thelight intensity through filters corresponding to red, green, and blue,and the controller 30 calculates the light intensity by converting itinto a density value. The controller 30 selects a patch image in whichthe density value is predetermined value stored in the ROM 32 inadvance, and automatically enters the level of the secondary transfervoltage corresponding to the patch image as a level of the secondarytransfer voltage on the screen illustrated in FIG. 4B).

In the present embodiment, although the spectroscopic sensor 90 isdisposed on the conveyance path of the sheet S, the present invention isnot limited thereto. That is, for example, the spectroscopic sensor 90may be arranged on the upper part of the main body of the image formingapparatus A, and the sheet S on which the patch image is formed may beplaced on the spectroscopic sensor 90 and scanned by a user.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2019-012271, filed Jan. 28, 2019, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image forming apparatus comprising: an imagebearing member; a transfer member configured to transfer a toner imagecarried on the image bearing member to a sheet by being applied with avoltage; a controller configured to execute a mode of outputting a testchart for setting a voltage to be applied to the transfer member duringimage formation, the mode being a mode of transferring a plurality oftest images to the test chart by applying a plurality of differentvoltages to the transfer member; and an operation portion capable ofsetting a type of a sheet on which the mode is executed; wherein thecontroller is configured to preset a voltage value for setting a voltageto be applied when the test images are transferred in the mode based ona voltage value, which is set in the previous mode.
 2. The image formingapparatus according to claim 1, wherein the controller presets a centervalue for setting a voltage corresponding to a center of the voltages tobe applied in the mode based on the voltage value, which is set in theprevious mode.
 3. The image forming apparatus according to claim 2,wherein the center value preset can be change via the operation portion.4. The image forming apparatus according to claim 3, wherein thecontroller forms the plurality of test images by switching a voltage tobe applied to the transfer member by a predetermined value in apredetermined range around the center value.
 5. The image formingapparatus according to claim 1, further comprising an image detectingunit configured to detect the test images, wherein the controller sets avoltage to be applied to the transfer member during image formationbased on a result of detection detected by the image detecting unit. 6.The image forming apparatus according to claim 5, wherein the imagedetecting unit outputs data relating to spectral reflectance of the testimages based on reflected lights reflected from the test images, and thecontroller sets a voltage to be applied to the transfer member duringimage formation based on the data.
 7. The image forming apparatusaccording to claim 5, wherein the image detecting unit is opticalsensor.
 8. The image forming apparatus according to claim 1, furthercomprising a current detecting unit configured to detect a value of acurrent that flows when a voltage is applied to the transfer member,wherein the controller has another mode for setting a voltage to beapplied to the transfer member during image formation based on arelationship between a voltage applied to the transfer member duringnon-image formation and a current detected by the current detecting unitat that time, wherein the controller sets the voltage to be applied tothe transfer member during image formation based on the voltage valueset in the mode and the relationship.
 9. The image forming apparatusaccording to claim 1, wherein the image bearing member is anintermediate transfer belt onto which a toner image formed on aphotosensitive member is transferred.